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* [Bug tree-optimization/96020] New: FRE uses not available def across EH edges
@ 2020-07-01 14:30 rguenth at gcc dot gnu.org
2020-07-01 14:31 ` [Bug tree-optimization/96020] " rguenth at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-07-01 14:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96020
Bug ID: 96020
Summary: FRE uses not available def across EH edges
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
I failed to distill a small testcase like
int *q;
int main()
{
int *p = q;
int a = 1;
try {
a = *p;
} catch (...) {
int b = *p;
a += b;
}
__builtin_exit (a);
}
where a __cxa_begin_catch (_1); prevents CSE of the *p load across the EH
edge with -fnon-call-exceptions:
<bb 2> :
# VUSE <.MEM_4(D)>
p_5 = q;
# VUSE <.MEM_4(D)>
_7 = *p_5;
<bb 5> :
<L3>:
# VUSE <.MEM_4(D)>
_1 = __builtin_eh_pointer (1);
# .MEM_9 = VDEF <.MEM_4(D)>
__cxa_begin_catch (_1);
# VUSE <.MEM_9>
_10 = *p_5;
but for g++.dg/opt/pr92610.C and g++.dg/pr48633.C with for example -std=gnu++14
we can see it doing this:
<bb 6> :
_45 = MEM[(sizetype *)_28];
<bb 18> :
<L18>:
- _51 = MEM[(sizetype *)_28];
- _15 = _51 + 2;
+ _15 = _45 + 2;
_16 = _15 * 4;
operator delete [] (_28, _16);
resx 5
thereby ICEing with a new SSA verification piece I coded after directing
Martin to only consider the fallthru edge as insert location for the SSA
defs of an internally throwing stmt.
DOM is probably susceptible to this, too.
I'm not sure how to trigger a real-world case that would exhibit breakage
(for the above we're removing another trap on the EH handler side). A way
to trigger the odd IL seen for pr92610.C in a more controlled example
would be nice to have.
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/96020] FRE uses not available def across EH edges
2020-07-01 14:30 [Bug tree-optimization/96020] New: FRE uses not available def across EH edges rguenth at gcc dot gnu.org
@ 2020-07-01 14:31 ` rguenth at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-07-01 14:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96020
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Created attachment 48819
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48819&action=edit
the verifier
^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-07-01 14:30 [Bug tree-optimization/96020] New: FRE uses not available def across EH edges rguenth at gcc dot gnu.org
2020-07-01 14:31 ` [Bug tree-optimization/96020] " rguenth at gcc dot gnu.org
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